The invention relates to a method for preparing a solution from a solvent and an active substance in and on a disposable injector with a housing, with an at least intermittently fillable cylinder/piston unit which is arranged thereon and has a manually movable piston, and with a detachable container adapter mounted upstream of this cylinder/ piston unit, wherein the container adapter supports a container which can be filled at least intermittently with active substance and which is closed by an openable stopper.
WO 00/23133 discloses, among other things, an injector of this kind. Between the container partially filled with lyophilisate and the cylinder/piston unit, which here is a cartridge closed at the front by means of a lid and at the rear by means of a piston, a needle carrier with a twin-end injection needle sits in the container adapter. By pushing the container forwards into the container adapter, the front end of the needle pierces the seal of the container. By screwing the container adapter into the injector, the rear end of the needle pierces the lid of the cartridge. The needle carrier is at the same time permanently adapted to the cartridge. The liquid in the cartridge is pumped into the container, where the lyophilisate dissolves. The solution is then pumped back into the cartridge. After removal of the container adapter, the spring of the injector is tensioned manually in order to make this ready for injection.
The object of the present invention is to develop a method for making a solution using a modular disposable injector which stores a liquid and an active substance in each case separately and in a sterile manner and which provides a space in which the active substance, for its application, is dissolved in the liquid or mixed with the liquid.